Method of treating exhaust gases of internal combustion engines



United States Patent O 6 Claims. (Cl. 23-2) This application is adivisional of our co-pending application U.S. Ser. No. 109,483, filedMay 19, 1961, now Patent No. 3,216,954, issued Nov. 9, 1965.

Application Ser. No. 109,483 is a continuation-impart of our thencopending application U.S. Ser. No. 59,392, filed Sept. 29, 1960 and nowabandoned, which is a continuation-impart of our then copendingapplication U.S. Ser. No. 828,778, filed July 22, 1959, and nowabandoned.

This invention relates to the treatment of combustion productscontaining nitrogen oxides, carbon monoxide, and hydrocarbons and ismore particularly directed to the catalytic treatment of automobileexhaust gases by passing the gases over a mangano-chromia-manganitecatalyst.

In the catalytic treatment of automobile exhaust gases, it isimpractical to use catalysts that require a high exhaust gas temperatureto initiate reaction because automobiles operate much of the time incity driving and at comparatively low exhaust temperatures. Themanganochromia-manganite catalysts used in the present inventionlight-off at relatively low temperatures even after extended use so thatthey are practical and effective under ordinary conditions of motorvehicle operation. The catalysts used in this invention are alsoeffective in fusing the operation of catalysts which require a higherlight-off temperature because the manganite catalysts begin operating ata low temperature and heat the catalyst bed and exhaust stream.

The determination of light-off temperature is difficult because it isnot a definite figure but rather depends upon a variety of operatingconditions such as gas composition, gas velocity, heat losses, and thelike.

Light-off temperatures mentioned herein are determined arbitrarily bypassing a 1% ethane gas over the catalyst and are defined as thetemperature required to oxidize 90% of the ethane. This is taken as thelightoif temperature because it is thought it will bear a closecorrelation to the actual temperatures of light-oif in operation.

Catalysts effective for treatment of waste gases resulting from thecombustion of hydrocarbon fuels are ordinarily extremely sensitive towater. Liquid Water, as Well as water vapor, is found in the exhaustgases of motor vehicles and in other such combustion systems. The liquidwater causes spalling of the catalyst and weakens them mechanically somuch that after very short periods of operation they are no longeruseful. The manganochromia-manganite catalysts used in the presentinvention are quite resistant to damage from liquid water and watervapors.

Moderately effective systems have been devised for the handling ofexhaust gases of motor vehicles providing the motors are operated oncarefully selected fuels. A commercially satisfactory catalyst should beresistant to lead, sulfur, halogens, phosphates, boron, and theirreaction products, and to hydrocarbon fuels and oils and their partialcombustion products. Such a catalyst should also be resistant tomanganese compounds which are sometimes used as anti-knock agents. Thecatalysts used in the present invention have remarkable resistance tosuch constituents often found in auto exhaust. They are also quiteresistant to deactivation by high temperatures because of theircomposition and structure.

It is imperative that a satisfactory catalyst be effective for theoxidation or reduction of as many as possible of the numerous componentsin the waste gases being treated. The mangano-chromia-manganitecatalysts used in the present invention are effective in converting thenitrogen oxides, carbon monoxide, the hydrocarbons, and other exhaustgas components and are thus broadly effective.

It will be noted that some catalysts used in the invention are somewhatless efiective in converting nitrogen oxides than others but they arenevertheless valuable for the conversion of carbon monoxide andhydrocarbons.

It will be seen that exhaust gases can be converted in a plurality ofstages. Thus the reduction of nitrogen oxides can occur in a first stageand then oxygen can be added in the second stage for the oxidation ofcarbon monoxide and hydrocarbons. The same or different catalysts can beused in the two or in the plurality of can be used. As mentionedeariler, the addition of air at a later stage may assist in reaching alight-01f temperature since the air if introduced sooner would otherwisehave a cooling effect.

It is imperative that a satisfactory catalyst have a reasonably smallvolume so that it can. be conveniently carried by a motor vehiclewithout requiring an unreasonable amount of room. Another practicalconsideration is that the catalyst should have a reasonably long servicelife, though this can be balanced somewhat against low cost. Thecatalysts used in the present invention are relatively inexpensive, havea surprisingly long life, and are effective in relatively small amounts.

The 'mangano-chromia-manganites used in the method of this invention aredescribed in detail and claimed as catalysts as such and withco-catalysts, interspersants, and supports in our copending parentapplication identified in the first paragraph above. The entiredisclosure of the parent application is hereby incorporated byreference. A general description of the catalysts should be sufficienthere.

The mangano-chromia-manganites have the following empirical chemicalcomposition:

XCr O 2YMnO in which n can be 2, 3 and 6 and m can be 1, 1.33, 1.5, 2and 2.5. The Mn:Cr ratio can vary from 3:05 to 3:30. The atomic ratio,that of YrX, is substantially the same and thus when Y equals 3, X canequal 0.5 to 30.

The empirical formula is a summation of the proportion of the content ofMnO, M Mn O Mn O Cr O Cr O M1102, CIO 'Ml1203, M 0 Cr O MnO in thecatalyst.

In addition to the above oxides, a mangano-chromiay 3,316,057 PatentedApr. 25, 1967 present invention, it is much preferred to use those inwhich the ratio of Y:X is either above 3:3 or below 3:2. The weightratio of YzX, that is MnzCr, is preferably 3:05 to 321.5 and 3:3.5 to3:30. Mangano-chromiamangani-tes thus constituted are far more valuableand thermally stable as catalysts than those having a ratio of 3:2. to3:3 and can be used even without the interspersants which will bedescribed hereafter. If the ratio is around 3:2 to 3:3 interspersantsmust be used.

A mangano-chromia-manganite having a ratio of MnzCr of 3:2 can beprepared according to the method of Wortz US. Patent 2,108,156. Theproducts are designated there as manganese chromites. This designationcan be used forv the catalysts used in this invention when the MnzCrratio is 3:0.

Mangano-chromia-manganites having the full range of ratios of manganeseto chromium can be prepared by procedures described in detail in ourcopending parent application. Generally it can be said that they areprepared by reacting appropriate salts of manganese and chromium inaqueous solution. Thus, manganese nitrate and chromic acid anhydride aredissolved in water and ammonia is added to make a precipitate. Theproducts of high manganese ratio can be prepared by adjusting theamounts of components but a high chromium product can be made when ahexavalent chromium salt is used as a chromium source only by addingfurther chromium compounds such as ammonium chromate to the precipitatethus prepared after filtration. Alternatively the appropriate proportionof suitable salt such as manganese nitrate with chromium nitrate can beprecipitated or fused together to give mangano-chromia-manganites of thedesired MnzCr ratio.

The mangano-chromia-rnanganite precipitates preferred according to theinvention have a crystallite size no greater than 1000 Angstroms.Preferred catalysts can have a greater crystallite size as hereinafterdiscussed. The fact that the mangano-chromia-manganite is crystalline inform can be determined by conventional X-ray analytical techniques ascan the order of crystallite dimensions. A suitable method is shown inX-ray Diffraction Procedures by H. P. Klug and L. E. Alexander,published by John Wiley & Sons, New York, 1954 edition. The preferredmangano-chromia-manganites of the invention have a crystallite sizeranging downwardly from about 50 Angstroms or more broadly from about400 Angstroms. The size will fall in the range below that figure anddown to sizes where only a few molecules are associated but enough toestablish a crystal pattern. The structure is inferable from electrondiffraction, X-ray diffraction, or electron-micrograph, the mostapplicable method being dependent upon the crystallite size.

It is to be noted that X-ray diffraction and electron diffraction arenot too informative if a particular catalyst contains large crystallitesas well as small crystallites of the catalytically active materials. Thelarge crystallites obscure the presence of the small which maynevertheless be present in amounts sufficient to make the catalystsatisfactorily effective-say even as low as 5 to In this event,crystallite size must be determined by another method such aselectron-micrograph. Thus there is no objection to having largecrystallites present in a catalytic aggregate of the invention providingonly that there are a sufficient number of crystallites in the sizeranges herein described so that the catalyst is suitably active and sothat the interspersants are effective. In other words, crystallites ofmangano-chromia-manganite, co-catalyst, and interspersants which arepresent in sizes well outside of the preferred ranges can be regarded asdiluents which are largely inert and if not present in too large amountare not objectionable.

After catalysts have been in use for some time the crystallite sizerises to considerably higher figures. When the. size has risen to about900 Angstroms the catalyst will be about one-half as effective as whenit was put in service with a crystallite size around 50 Angstroms. One.may initially use a catalyst in which the crystallites have a size up to1000 Angstroms with a loss of effectiveness which can be compensated byusing a larger amount of catalyst. Of course, the effectiveness dropsoff with further use and such catalysts are less desirable economicallythan those of smaller crystallite size as noted.

While it is greatly preferred to use mangano-chromiamanganite catalystsin which the crystallite size is initially below 1000 Angstroms andafter use is still below 1000 Angstroms, economics will sometimesjustify the use of catalysts with larger crystallite sizes. Thus amanganochromia-manganite of low MnzCr ratio and containing no addedinterspersant can be made quite inexpensively and after heating to about800 C. for three hours or so will have a crystallite size by X-ray ofaround 1500 Angstroms. Even such a product shows considerable activity.Even higher crystallite sizes up to 2000 or even 2500 Angstroms or evenhigher can be used if low activity can be offset by other advantagessuch as low cost or if high reaction temperatures can be used. These arenot, however, the most preferred catalysts of the invention.

It is noted that when it is said that crystallite size is less than 50Angstroms, this means that using the X-ray or electron microscopetechniques now available one obtains this apparent crystallite sizedetermination. Actually some workers might obtain a figure of the orderof, say, 60 or Angstroms using the same techniques and the same sample.

Catalysts used according to the present invention can be composedessentially of mangano-chromia-manganite prepared as above andcontaining an interspersant as described below. It is preferred,however, that it be promoted and further modified with a secondinterspersant as described below.

Preferred catalysts for use in the invention contain a second catalystin addition to the mangano-chromia-manganites. This can be any catalystor mixture which has value. in treating the gases converted according tothe invention such as lead chromate, magnesium chromate, bariumchromate, and strontium chromate. It is preferred to use base metalcatalysts which are base metal chromites of Copper Cadmium Nickel CobaltIron Tin Zinc Bismuth A co-catalyst can be selected from those shown inLazier US. Patent 1,964,001 and the combination ofmanganochromia-manganite with the co-catalyst can be prepared asgenerally there described. However, it is suggested in the patent that achromite mixture be heated to temperatures to make a mixedoxide-chromite product at temperatures in excess of 600 C. and this willresult in sintering and reduction of catalytic efficiency. This aspectof the teachings of the patent should not be followed in makingpreferred catalysts of the present invention.

The base metal catalyst chromites are prepared in the same generalmanner as above described for manganochromia-manganites. Thus awater-soluble salt of one of the base metals as above mentioned isdissolved in the same solution with the manganese and chromium compoundsas originally described and coprecipitated with them. The soluble saltscan be the chlorides, sulfates, acetates, or nitrates of any of the basemetals mentioned. Again, the amount of the chromium compound dissolvedshould of course be adequate to produce a proper ratio with the basemetal. This should be a stoichiometric amount.

The precipitants mentioned above for precipitatingmangano-chromia-manganite, such as ammonia, can at the same time effectcoprecipitation of the base metal catalyst.

The crystallite size of the catalyst precipitate should be in a sizerange as already described for the manganochromia-manganite precipitatesand as there stated should preferably be no greater than 1000 Angstromsand is preferably under 400 Angstroms and, even better, is less than 50Angstroms.

Instead of being coprecipitated with the manganochromia-manganite, thebase metal precipitate can be separately formed by use of astoichiometric amount of the chromium compound and precipitation as withammonium hydroxide or anhydrous ammonia. The two slurries thus formedcan be brought together or the precipitates separately prepared can bedried, calcined and thereafter mixed. This latter, however, is not apreferred practice.

The proportions of manganite to the base metal catalyst can be widelyvaried. Generally the ratio of manganese to base metal should be about1:1 and can range from 1: to 10:1 or even higher.

The process conditions used in the precipitation ofmangano-chromia-manganite and, if used, the base metal catalyst shouldbe controlled in order to obtain crystallites in the size range alreadyindicated. Those skilled in the art are familiar with the processvariables which result in differing particle sizes and so there is nogreat difficulty in obtaining crystallites of the sizes desired. Ingeneral, it may be said that to obtain small crystallites acomparatively low temperature is preferred, say room temperature, or asolution may even be cooled somewhat, particularly in warm weather. Thepresence of local overconcentration of the anhydrous ammonia or otherprecipitant should be avoided by rapid stirring or agitation. Again,this is well understood in the art. When it is understood what result isto be obtained, one skilled in the art can readily achieve it.

The preciptation should also be effected from a comparatively dilutesolution. Ordinarily there should be used about one molar concentrationwith respect to the water, of the manganese salt, the chromium compound,the copper compound, and other materials to be coprecipitated. If muchhigher concentrations are used there is a tendency to favor theproduction of larger crystallites. Dilute solutions are also valuablebecause occlusion of impurities is minimized.

It will be understood that while the crystals are formed in the particlesizes desired, they precipitate as aggregates and agglomerates ofloosely associated crystallites which can be separated from water as byfiltration, centrifugation, or decantation.

While reference has been made above primarily to the use of co-catalystswhich are coprecipitated chromates, it will be understood that catalyticmetals can be added to the mangano-chromia-manganite catalyst systems invarious forms. Thus they can be added as the oxides, carbonates,acetates, oxalates, or in any other form in which they have catalyticactivity or can develop catalytic activity upon calcination. Thuscompounds such as the fol-. lowing can be used as precipitates which areformed separately though in every instance it is preferable that they bein a particle size range such that the crystallite size is as describedherein:

Copper oxide Nickel oxide Iron oxide Zinc oxide Cadmium oxide Tin oxideBismuth oxide Manganese oxide or dioxide As just noted above, thecorresponding hydroxides can be used.

The mangano-chromia-manganite particles in catalysts of the inventionhave a tendency to grow in size. This growth occurs either bycrystallite growth or by agglomeration, and the tendency is particularlygreat in use when ency to agglomerate with the base metal catalyst,though.

this is not perhaps as great as the tendency to crystal growth.

To hinder such growth, preferred catalysts of the invention containinterspersants. These are comparatively inert particles of sizecomparable to that of the crystallites of the mangano-chromia-manganite.The interspersant is intimately associated with the manganite andco-precipitated co-catalyst, if any, and, being of a different crystalhabit and size, hinders agglomeration and crystallite growth in laterphases of the catalyst preparation and use.

The interspersant has the function as will be seen and which will bediscussed further of keeping the crystallites of the catalyst and theco-catalyst apart. The interspersant could somewhat less aptly be calleda dissident and they are randomly distributed among the crystallites ofthe catalysts. Generally, it may be said that the interspersant can beany refractory material, .the crystallites of which are similar in sizeto those of the mangano-chromiamanganite. The interspersed refractoriesshould have a melting point above 1000 C. and more preferably above 1600C.

The interspersants which can be used include such water-insolubleprecipitates as:

(1) Aluminum oxide and hydroxide (2) Titania (3) Thoria (4) Ceria (5)Chromi'a (6) Magnesia (7) Calcium oxide and hydroxide (8) Barium oxideand hydroxide (9) Strontium oxide (10) Zinc oxide (11 Manganese oxide(12) Silica (13) Beryllia (14) Zirconia (l5) Lanthana (16) HafniaAluminum hydroxide, which is present as oxide in the final product ispreferred. Manganese oxide and chromia are listed as interspersants tobe added in amounts exceeding those which would be present in themanganochromia-manganite of the ratios described.

Other insoluble compounds of the above metals can be similarly used suchas barium chromate, calcium chromate, chrome oxides, calcium silicates,barium silicates, and magnesium aluminate. There can be used still othersuch insoluble compounds of the metals listed such as barium titanate,calcium titanate, manganese carbonate, aluminum chromite, magnesium,calcium, strontium and barium as silicates, aluminates, titanates,zirconates, and cerates.

It will be understood that some of the interspersants especiallyexcesses of manganese oxide and chromia will have catalytic activity oftheir own, though this is not the primary reason for including them inthe aggregates of the invention.

If the catalysts are to be used at temperatures which can be closelycontrolled and will not greatly exceed 700 (3., silica can be used as aninterspersant. Silica can be used in the form of any of the finelydivided colloidal products such as silica sols or aerogels in which itis commercially available.

It will be understood that while the interspersant will normally be inthe form of the oxide in the final catalyst aggregate after calcination,the crystallites can be introduced in the form of heatdecomposablesalts. They can be formed in situ in the presence of themangano-chromiamang'anite catalyst and in the presence of theco-catalyst. Such heat-decomposable products can be used as:

Particles which can readily be introduced in the form of sols ordispersions in addition to those already listed above are:

Magnesium oxide and hydroxide Titanium oxide, sol and gel Aluminumalcoholates Zircon powder Aluminum hydroxide gel Zirconia gel Ceriumoxide (8) Silica sol (9) Zinc oxide and hydroxide (l) Strontiumhydroxide and oxide The ultimate particle size of the interspersants isas already described for the mangano-chromia-manganite precipitatesabove and is preferably less than 1000 Augstroms, preferably not morethan 400 Angstrorns, and it is still more preferred that the size beless than 50 Angstroms. Precipitates may be amorphous or crystalline,and for the purposes of the present invention this is comparativelyunimportant so long as the ultimate paritcle size is of the correctorder.

The methods of production of interspersants in suitable form requires noextended discussion because the pre paration of colloidal dispersions ofthese types is well understood.

The interspersant can be used in widely varying amounts 'and can rangefrom, for example, to, say, 75% based upon the total weight of solids inthe final precipitate or mixture of mangano-chromia-manganite plus basemetal catalyst, if there is one present.

The coprecipitates or mixtures prepared as above are then calcined toproduce a somewhat more porous structure. Calcination can be conductedat any of a wide range of temperatures from about 350 C. up to 500 C. oreven higher. The temperature should in any event be below that at whichsintering occurs and it should be sufficiently high to effectdecomposition of the hydrates present.

After calcination, products as prepared above have somewhat openstructure as described. They are preferably stabilized by, theintroduction into the structure of a second interspersant which is arefractory of a particle size suitable for such introduction. Thuschromic oxide, magnesium hydroxide and any of the interspersants asabove described are introduced as a sol or a water-soluble salt whichcan be decomposed in situ.

For formation in situ one can use such water-soluble salts as thosepreviously described as interspersants. It will be understood that thecatalyst aggregates of the invention will contain the interspersants ina form of oxides because of the calcination which is part of the processof preparing such aggregates.

The particles of the second interspersant should preferably be withinthe size ranges previously described. Thus the particles should have asize under 1000 Angstroms, preferably not greatly in excess of 400Angstroms and even better should be no larger than 50 Angstroms. Somesuch particles can be included which are larger, but they will servemore as supports than as second interspersants. It is observed that thesecond interspersant is ordinarily added after the catalyst aggregatehas taken form and has been dried. Such second interspersants can alsobe termed structural stabilizers.

The second interspersant can range in amount from 0.5% to or so byweight of the combined weight of catalyst including the firstinterspersant.

When crystallite or particle size is mentioned it Will be understoodthat the size intended is the average of the largest dimension. This ismeasured by X-ray or, for larger particles or for mixtures of sizes, canbe measured and counted in an electron micrograph.

It is to be observed that the crystallite size of interspersants and ofthe catalyst, as well as of the manganechromia-manganite should all bebelow 1000 Angstroms and more preferably below 400 Angstroms, and evenbetter under 50, as described generally elsewhere. It is further to benoted that it is advantageous to select an interspersant, a catalyst,and a second interspersant all of which have a different crystal habitfrom each other and from the mangano-chromia-manganite. It should alsobe observed that while it is greatly preferred to add a secondinterspersant after a drying or calcination step as described, one caninstead in forming the catalyst aggregate use two interspersants whichare heteromorphic, that is of different crystal habit. More than two canbe used in either or both stages.

While it is much preferred, as just stated, that the interspersants allbe of different habits, it is possible to make usable and valuablecatalysts in which this is not true.

It will be noted that while we speak frequently of a secondinterspersant this is language adopted to refer to an interspersantadded after the drying and calcination. It is not essential that therealways be a first interspersant as will be illustrated in the examples.It is also to be observed that when manganese oxide or chromia are usedas a second interspersant they can become a part of the spinel phase ifthe temperatures go high enough in subsequent heat treatments of thecatalyst. Such temperatures are usually considerably in excess of thoseencountered in manufacture or use of the catalyst of the invention sothat when added at this stage the manganese oxide or chromia can beregarded as serving primarily as interspersants rather than as part ofthe spinel phase.

Catalysts prepared as above described can be supported in the. waysalready well understood in the art. Thus, they can be applied asslurries to conventional supports and heat-treated as will hereinafterbe described.

Suitable supports and carriers are:

(1) Porous ceramic spheres, tablets, or rings which have a softening ormelting point in excess of 1200 C.

(2) Etched nickel, Nichrome, and Inconel Wire (3) Alundum (4) Pumice (5)Diaspore (6) Bauxite (7) Periclase (8) Zirconia (9) Titania l0):Diatomaceous earth (11) Calcium sulfate (12) Barium oxide (13) Calciumoxide (14) Activated alumina granules The catalysts can also 'be appliedto such a carrier or support by applying fusible compounds of themanganese, chromium, co-catalyst, and interspersant and fusing asgenerally above described.

The refractory is preferably heteromorphic to the catalyst and so far aspracticable to interspersants in the refractory. Among the refractorysupports discussed, the following when having appropriate surfaces canadvantageously be used:

(1) Bauxite (2) Zirconia (3) Titania (4) Activated alumina.

To obtain the effects describe-d, the surface area ought to be at least10 M /g. with pore dimensions such that 40% are less than 200 Angstroms.Surface area and pore diameter are determined by standard methods usedin catalysis and elsewhere. It is more preferred that the surface areabe at least 80 M /g. with pore dimensions of at least 60% less than 200Angstroms.

The amount of catalyst to apply to such a refractory will depend uponthe surface area of the particular refractory selected. Ordinarily theamount will run from about 2% for refractories of comparatively lowsurface area up to around 20% for refractories of high surface area. Itwill be evident that there is no great disadvantage to using too muchcatalyst except that it is wasteful because catalytic efiiciency doesnot rise in proportion to the amount of catalyst used above a certainfigure which can readily be determined for a particular catalyst andsupport.

Catalysts prepared and supported as just described are illustrated inmany of the examples such as Examples 27 and 30 in which bauxite is usedas the support material. The bauxite as used in those examples has asurface area of about 200 M /g. and approximately 60% of the pores areunder 200 Angstroms diameter.

Instead of supporting the catalysts as just described, they can becompressed into tablets or pellets. This can be done with conventionalpelleting and tableting machinery. A pelleting lubricant should be used,such as powdered graphite or stearic acid. Other conventional lubricantscan be used, and the amounts are those normally employed, say 0.1 to 2%,the exact amount being determined in accordance with customary practice.

The heat treatment results in the product becoming more porous. Volatilematter leaves the catalyst as a result of thermal decomposition andthe-re is, more importantly, a structural orientation which brings thecrystallites closer together and leaves larger voids between the groupsof crystallites, all as seen in the drawing.

The temperature to be used should be selected to effect thismodification, but should not be so high as to result in sintering of thecatalyst components. More specifically, temperatures from about 250-800C. will be satisfactory. The heating must occur for long enough toeffect a desired degree of such orientation, and may vary from a fewminutes to several hours. At lower temperatures around 250 C. an hour orso may profitably be used and at around 400 C., which is a preferredtemperature, about 30 minutes or somewhat less is adequate. At stillhigher temperatures, times of only 5 or minutes are sufficient.

The catalyst products can contain widely varying amounts ofmangano-chromia manganite, interspe-rsant, second interspersant, andco-catalyst. In the final product, however, it can generally be statedthat the amount by weight of first interspersant plus secondinterspersant is approximately equal to and can range up to ten times asgreat as the mangano-chromia-manganite. If co-catalysts are present theywill ordinarily amount to from twice as much to one-tenth as much on amolar basis as the mangano-chromia-manganite.

It is to be noted that the life of catalytic aggregates can be extendedby the inclusion of small amounts of an alkali or an alkaline earth.These have the effect of permitting the catalyst to regenerate itself inuse through their functioning as a promoter for the re-oxidation of themangano-chromia-manganite to a higher state of oxidation. Thus, based onthe weight of mangano-chromia manganite, there can be used between 0.05%and 10% of an alkali. The alkalis can include potassium, sodium,lithium, magnesium, calcium, strontium, and barium hydroxides, oxides,or carbonates. The alkali can be added 10 at any appropriate stage inmanufacture or after the catalyst has been finished. Again, the alkalican be added to a catalytic support.

The heat-treatment as described ordinarily causes a slight weakening ofthe pellets or supported catalyst. The temperature at no time goes highenough to result in a sintering which will strengthen the catalyst. Thetreatment, however, markedly increases the value of the catalyst andparticularly increases its resistance to spalling in the presence ofliquid water. As a consequence, the catalyst is resistant to watercarried by the exhaust gases, to water which it may encounter in storageor in handling, and to water or water solutions which may be used forwashing the catalyst to regenerate it after a period of use. Thus, thecatalyst can be regenerated by washing with water or by washing withdilute, say around 10%, aqueous solutions of such acids as hydrochloric,nitric, acetic, formic and hydroxy acetic acids or with aqueoussolutions or dispersions of catalytically active compounds.

The products as produced above are characterized by having a crystallitesize preferably under 1000 Angstroms, preferably under 400, and betterunder 50, as above described. Additionally the products have thechemical characteristics above described which can be determined byX-ray or by conventional chemical analysis. Additionally the productsare porous and will have a surface area by gas adsorption of above 50 M/g. After use the catalysts will still have a comparatively high andeffective surface area and the catalyst, after heating to 800 C. forthree hours, will still have a surface area by gas adsorption in excessof 2 M /g. Surface area is measured by the BET method.

The method of the present invention can be carried out in catalyticconverters of types already designed including those for use on motorvehicles. Those skilled in the art can readily design a suitableconverter which ideally should mufile sound at least to some extent andshould provide for an adjustable air supply. The muffler in addition toacoustic insulation can also be insulated either interiorly orexten'orly with heat insulation so that the temperatures will reach thelight-off temperatures as soon as possible.

In order that the invention may be better understood, reference shouldbe had to the following illustrative examples:

EXAMPLE 1 (1) Dissolve 165 pounds, 3 pound moles, of metallic manganeseas the nitrate in 750 gallons of water. That is to say, manganesenitrate is used (containing 165 pounds Mn) in amounts of 3 pound moles.

(2) Dissolve also in the same solution containing the manganese nitrate300 pounds, 3 pound moles, of chromic acid anhydride (CrO (3) Adjust thevolume to 800 ture to 35 C.

(4) Agitate the solution vigorously while adding vaporized anhydrousammonia through a diffusion sparger at a rate of two pounds per minuteuntil the precipitation is complete. Further addition of ammoniaproduces no further precipitate.

(5) Agitate the slurry for one hour then filter in a plate and framepress. Wash the filter cake in situ to remove dissolved salts.

(6) Dry in thin layers at 150 C. for 16 hours.

(7) After drying, calcine the catalyst at 400 C. for three hours afterreaching this temperature. Manganochromia-manganites thus prepared had acrystallite size of 50 Angstroms or less.

(8) Knead a 40 pound lot with 65 pounds containing 128 pounds ofammonium chromate. The resulting mangano-chromia-manganite had theformula XCr O -ZYMnO in which the ratio of Y:X is 3:12 and n has thevalues of 2, 3, and 6 and m of 1, 1.33, 1.5, 2, and 2.5. The developmentof the mangano-chromiamanganite crystals and of the values of n: and mcomes gallons and the temperaof water about during the subsequentdrying, heating and calcining.

(9) Pulverize, mix with 1% of finely divided graphite and pill on aStokes BB-2 rotary tableting machine.

(10) Heat the pellets thus obtained in thin layers in an oxidizingatmosphere at 400 C. for three hours. The catalyst pellets as thusprepared can be used in an automobile exhaust, either alone or withother catalysts, for abatement of the exhaust-fume problem.

Mangano-chromia-manganite catalysts as prepared above have crystalliteswhich are largely in the form of cubes. They are very small but if thecatalyst as prepared, prior to pelleting, is heated at 600 C. for threehours and then prepared for an electronmicrograph in the usual way, theelectronphotomicrograph shows that substantially all of the discreteparticles are cubes.

EXAMPLE 2 Proceed with catalyst preparation as in Example 1 through Step7 and then follow the following procedure:

(8) Knead 100 poundsof material prepared as above with 65 pounds ofwater in which is slurried, and partially dissolved, 10 pounds ofmagnesium oxide.

(9) Dry, pulverize and mix the product thus prepared with 1% ofgraphite, and pellet.

(10) Heat the pellets thus obtained at 400 C. for three hours. Thecatalyst pellets thus prepared can be used for fume abatement accordingto the invention.

EXAMPLE 3 Catalyst preparation proceeded as in Example 1 through Step 7and then:

(8) Knead 100 pounds of material prepared as above with 65 pounds ofwater. in which there is dissolved 13 pounds of ammonium chromate.

(9) Dry, pulverize and mix with graphite, and pill.

(10) Heat the pellets thus obtained at 400 C. for three hours. Catalystpellets thus prepared can be used for fume abatement according to theinvention.

EXAMPLE 4 Catalyst preparation proceeded as in Example 1 through Step 7and then:

(8) Knead 100 pounds of material prepared as above with 65 pounds ofwater in which there is dissolved 10 pounds of magnesium chromate.

(9) Dry, pulverize, mix with graphite, and pill.

(10) Heat the pellets thus obtained at 400 C. for three hours. Thecatalyst pellets thus prepared can be used for fume abatement accordingto the invention.

EXAMPLE 5 (1) Dissolve 110 pounds, 2 pound moles of metallic manganeseas the nitrate in 750 gallons of water. Dissolve also in this samesolution 32 pounds, 0.5 pound mole, of copper as the nitrate and 30pounds, 0.5 pound mole, of nickel as the nitrate.

(2) Slurry in this solution 200 pounds of alumina hydrate, 0.5 micronsize, low soda content.

(3) Dissolve also, in the same solution containing the manganese andcopper nitrates and alumina hydrate, 300 pounds, 3 pound moles, ofchromic acid anhydride (CrO (4) Add water to bring the volume to 800gallons and heat to raise the temperature to 35 C.

(5) Agitate vigorously while adding vaporized anhydrous ammonia througha distributor at two pounds per minute until precipitation is completeas evidenced by further addition of ammonia producing no furtherprecipitation.

(6) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(7) Dry the filter cake at 135 C. for one hour.

(8) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the manganate salts tomangano-chromia manganites having a crystallite size of about 50Angstroms. The alumina and copper chromite formed are of similar s1ze.

(9) Charge 21 pound lot produced as above, together with 65 pounds ofwater in which is dissolved 13 pounds of ammonium chromate into asigma-arm mixer and knead until the mass is homogenous and clay-like.

(10) Dry and pulverize the product and mix with 1% of finely dividedgraphite. Pellet to form 3/16 by 3/16 inch cylindrical tablets.

(11) Heat the pellets in air at 400 C. for three hours to efiectstructural orientation without significantly increasing the crystallitesize of the mangano-chrornia manganite, the alumina, the copper chromiteor the chromic oxide contained.

Twenty-five pounds of a product prepared as above and using thirteenpounds of ammonium chromate in Step 9 is placed in a muffler designedfor catalytic conversion of exhaust gases of an automobile. An aircompressor driven by the car motor supplies about excess, or more, overthat stoichiometrically required for the oxidation of the exhaust gases.

The space velocity of the gases varied, depending upon motor speed,between 1,000 and 20,000. The light-off temperature of the catalyst isno higher than 260 C. and this temperature is reached initially byoperating the motor at a fast idling speed. The catalyst Operationcontinues between 425 and 650 C. It is noted in this connection thatoperating temperatures around 315 to 370 C. are more nearly ideal forlong catalyst life and can be achieved by appropriate heat exchange andinsulation of the rnufller equipment.

After 341 hours of motor operation at variable speeds the catalyst stilleffects 80% conversion of the hydro carbons and more than thatconversion of carbon monoxide. Nitrogen oxides were not converted to anygreat extent. Less than 10% of the catalyst is lost after 341 hours andit is apparently in good hysical condition. The catalyst can continue tooperate for a longer period.

The catalyst can be used for reduction of nitrogen oxides by appropriatecontrol of operating conditions. If the catalyst temperature is around515 C. and air is not introduced with the exhaust gases but is addedlater, then in the reducing section before air addition typicalconversions of nitrogen oxides are as follows:

Parts per Million of Nitrogen Oxides in Exhaust Gases Entering ConverterEfiiuent Gases an wHmen The catalyst prepared using a larger amount ofammonium chromate in Step 9 leads to similar results.

EXAMPLE 6 EXAMPLE 7 Prepare a catalyst as in Example 5 except that inStep 9 use ten pounds of magnesium hydroxide instead of ammoniumchromate.

Catalyst pellets prepared according to the procedure can be used forfume abatement as above described.

The catalyst has a light-01f temperature of 280 C.

13 After 48 hours of operation at an artificially high temperature of815 C. it still shows 76% conversion of hydrocarbons.

EXAMPLE 8 1) Dissolve 110 pounds, 2 pound moles, of metallic manganeseas the nitrate in 750 gallons of water. Dissolve also in the solution 63pounds, 1 pound mole, of copper as the nitrate.

(2) Slurry 200 pounds of alumina hydrate in the solution.

(3) Dissolve 300 pounds, 3 pound moles, of chromic acid anhydride in thesolution.

(4) Add Water to bring the volume to 800 gallons and heat to raise thetemperature to 35 C.

(5) Agitate vigorously while adding vaporized anhydrous ammonia througha distributor at two pounds per minute until precipitation is completeas evidenced [by further addition of ammonia producing no furtherprecipitation.

6) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(7) Dry the filter cake at 135 C. for one hour.

(8) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the manganate salts tomangano-chromic manganites having a crystallite size of about 50Angstroms. The alumina and copper chromite formed are of similar size.

(9) Charge a 100 pound lot produced as above, together with 65 pounds ofwater in which is dissolved 13 pounds of ammonium chromate into asigma-arm mixer and knead until the mass is homogeneous and clay-like.Alternatively a similar product can be made using 33 pounds of ammoniumchromate in this step.

(10) Dry and pulverize the product andmix with 1% of finely dividedgraphite. Pellet to form by 5 inch cylindrical tablets.

(11) Heat in air .at 400 C. for 3 hours.

Catalysts as thus prepared and using 13 pounds of ammonium chromate inStep 9 had a very low light-off temperature with ethane of 145 C. Thelight of temperature was 90 C. with 90% conversion with 1% carbonmonoxide instead of ethane. They can be used for fume abatementaccording to the invention. Similar results are obtained using 33 poundsof ammonium chromate in Step 9.

EXAMPLE 9 Proceed as in Example 8 except that in Step 9 use pounds ofmagnesium chromate instead of the ammonium chromate. The light-ofi?temperature of catalyst pellets thus made is about 250 C. They can beused according to the invention for fume abatement.

EXAMPLE l0 Proceed as in Example 8 except that in Stepe 9 use 10 poundsof magnesium hydroxide instead of the ammonium chromate. Catalystpellets thus prepared can be used for fume abatement according to theinvention.

EXAMPLE 1 1 (l) Dissolve 110 pounds, 2 pound moles, of metallicmanganese as the nitrate in 750 gallons of water. Dis s-olve also inthis same solution 32 pounds, 0.5 pound moles, of copper as nitrate and30 pounds, 0.5 pound moles, nickel as nitrate.

(2) Add 200 pounds of alumina hydrate, 0.5 micron size, to the solution.

(3) Precipitate the manganese, nickel and copper by adding sutficientvaporized anhydrous ammonia to effect complete precipitation asdetermined by absence of formation of precipitate on addition of furtherquantities of ammonia.

(4) Add to the slurry 309 pounds, 3 pound moles, of chromium hydroxidepowder, Guignets Green.

(5) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(6) Dry the filter cake at 135 C. for one hour.

(7) Raise the temperature of the dried product to 400 C. and calcine .atthat temperature for one hour to convert the manganate salts tomangano-chromia manganites having a crystallite size of about 50Angstroms.

(8) Charge a pound lot produced as above, together with 65 pounds ofWater in which is dissolved Water containing 13 pounds of dissolvedammonium chromate and into a sigma-arm mixer and knead until the mass ishomogeneous and clay-like. Alternatively a similar product can be madeusing 33 pounds of ammonium chromate in this step.

(9) Dry and pulverize the product and mix with 1% of finely dividedgraphite. Pellets to form by inch cylindrical tablets.

(10) Heat the pellets in air at 400 C. for three hours to effectstructural orientation without significantly increasing the crystallitesize of the mangano-chromia manganite contained. The catalyst as thusprepared can be used in an automobile exhaust for fume abatement.

EXAMPLE 12 Proceed as in Example 11 except that in Step 8 instead ofammonium chromate, dissolve 1.0 pounds of magnesium chromate in thewater used. The catalyst thus prepared can be used for fume abatementaccording to the invention.

EXAMPLE 13 (1) Dissolve pounds, 2 pound moles, of metallic manganese asthe nitrate in 750 gallons of water. Dissolve also in this same solution32 pounds, 0.5 pound mole, of copper as the nitrate and 30, 0.5 poundmole, of nickel as the nitrate.

(2) Slurry in this solution 200 pounds of titania. The titania is apigment-grade of titanium dioxide, rutile form, and having a particlesize below 1 micron.

(3) Dissolve in the solution 300 pounds, 3 pound moles, of chromic acidanhydride.

(4) Add water to bring the volume to 800 gallons and heat to raise thetemperature to 35 C.

(5 Stir vigorously While adding vaporized anhydrous ammonia through adistributor until precipitation is complete.

(6) Stir the slurry and filter. Wash with Water. at C. for two hours.

7) Calcine at 400 C. for forty-five minutes. Manganochromia m anganitescontained in products thus prepared have a crystallite size of about 50Angstroms. Similarly, alumina has a crystallite size of about 50Angstroms and the titania has a considerably larger crystallite size andis about 100 to Angstroms.

(8) The dried product is kneaded in 65 pounds of water containing 13pounds of ammonium chromate.

(9) Dry and pulverize the product and mix with a suitable pelletinglubricant such as graphite, stearic acid, or another commonly usedpelleting or tableting lubricant.

(10) Heat the pellets in air at 400 C. for thirty minutes. The catalystas thus prepared can be used in processes of the invention for abatingthe fume nuisance of automotive vehicles and for similar purposes.

In Step 1 above the manganese nitrate can be replaced with an equalmolar amount of manganese acetate, manganese chloride, manganesesulfate, or a mixture of any two or more of these. In Step 3, similarly,the chromium can be added using three pound moles of chromium nitrate,chromium chloride, chromium sulfate, or a mixture of any two or more ofthem.

EXAMPLE 14 (I) Dissolve 110 pounds of metallic manganese as the nitrate,2 pound moles, in 750 gallons of water. Also dissolve 60 pounds of ironas the nitrate, 1 pound mole.

Dry

(2) To this solution add 200 pounds of alumina hydrate.

(3) Dissolve three pound moles of chromium nitrate in the solution.

(4) Add water to bring the volume to 800 gallons and raise thetemperature to 35 C. Stir vigorously While adding finely divided,hydrated calcium hydroxide. This addition is continued untilprecipitation is complete.

(5) Stir the slurry for one hour and then filter. Wash with water. Dryat 135 C.

(6) Calcine at 400 C. for three hours.

(7) Charge 100 pounds of the product produced as above together with 65pounds of water containing 13 pounds of ammonium chromate and knead.

(8) Dry and pulverize the product and pellet it.

(9) Heat the pellets in air at 600 C. for three hours. Pellets producedas above can be used in'processes of the invention for the abatment ofobnoxious and objectionable combustion products.

In the above example, Step 4 instead of using calcium hydroxide as aprecipitant, add magnesium hydroxide, barium hydroxide, ammoniumchromate, or anhydrous ammonia to eifect substantially completeprecipitation as described.

EXAMPLE (1) Dissolve 110 pounds, equivalent to 2 pound moles, ofmetallic manganese as the nitrate in 750 gallons of Water. It is notedthat in all of the examples distilled or de-mineralized water shouldordinarily be used it local water supplies are at all impure,particularly with respect to metallic impurities. Dissolve also in thesame solution 32 pounds of copper as the nitrate and pounds of nickel asthe nitrate.

(2) Slurry also in the above solution a slurry prepared by adding 300pounds of 60% nitric acid to a slurry of 300 pounds of alumina hydrateslurried in 300 gallons of Water.

(3) Prepare in a separate vessel a solution of 456 pounds of ammoniumchromate prepared by dissolving 300 pounds of chromic acid anhydride inwater to which has been added ammonia equivalent to 12 pound moles ofanhydrous ammonia.

(4) Transfer the ammoniacal ammonium chromate solution to the vessel inwhich the manganese, copper, nickel nitrate solutions are being rapidlyagitated at 35 C.

('5) Adjust the slurry, if necessary, to obtain complete precipitationby supplementary additions of anhydrous ammonia.

(6) Stir the slurry for one hour and then filter. Wash the filter cakewith water. Dry the filter cake at 135 C.

(7) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for 30' minutes. The crystallite size of the calcinedproduct was not determined because it was below the range ordinarilymeasurable by X-ray analytical techniques. Certainly the crystallitesize is well below 50 Angstroms.

(8) Charge a 100 pound lot produced as above together with 65 pounds ofwater in which is dissolved 13 pounds of ammonium chromate into a mixerand knead until homogeneous.

(9) Dry, pulverize, and pellet the product.

(10) Heat-treat the pellets in air at 400 C. for one hour. The catalystas thus prepared can be used in processes of the invention for treatmentof the exhaust of motor vehicles.

In the above example, the copper nitrate used in Step 1 can be replacedwith a molecularly equivalent amount of nickel nitrate. Similarly, thenickel can be replaced with an equivalent amount of copper nitrate.

The calcination Step 7 above can be effected at temperatures of 350,450, and 500 C. with substantially equivalent results.

Procedures as set out above can be modified by conducting theheat-treatment of Step 10 at 250 C. for five hours or at 800 C, forthirty minutes. The higher temperature results in crystallites of largersize and is less desirable. In this and in the other examples,crystallite sizes up to 400 and even 600 Angstroms can be reached andhave value.

EXAMPLE 16 (1) Dissolve 110 pounds of metallic manganese as the nitrate,2 pound moles, in 750 gallons of water. Dissolve also 32 pounds ofcopper as the nitrate, 0.5 pound mole, and 30 pounds of nickel as thenitrate, 0.5 pound mole.

(2) Dissolve also 300 pounds of chromic acid anhydride, 3 pound moles.

(3) Add water to bring the volume to 800 gallons and raise thetemperature to 35 C.

(4) Agitate vigorously while adding vaporized anhydrous ammonia untilprecipitation is complete.

(5) After precipitation is complete, add to the slurry as a very finelydivided powder, 200 pounds of calcium hydroxide. After completion of theaddition of the calcium hydroxide, continue the stirring for anadditional hour and then filter. Wash the filter cake with water.

(6) Dry the filter cake and then raise its temperature to 500 C. Calcinefor thirty minutes. The crystallite size of products prepared in thismanner are found to be less than 50 Angstroms.

(7 pounds of the product produced as above is charged, together with 65pounds of water in which was dissolved 13 pounds of ammonium chromate,into a mixer andkneaded.

(8) Dry and pulverize the product and pellet it.

(9) Heat-treat the pellets in air at 400 C. for three hours. A catalystprepared as just described can be used in processes of the invention.

In Step 5 above, instead of using calcium hydroxide, the same procedurecan be followed using the same amount by weight of finely dividedtitania in rutile or anatase crystal form, thoria, ceria, finely dividedchromite ore, magnesium hydroxide, calcium silicate, magnesiurnaluminate, barium hydroxide, or strontium oxide.

EXAMPLE 17 (1) Dissolve pounds of metallic manganese as the nitrate, 2pound moles, in 750 gallons of Water. Dissolve also in this solution 59pounds of cobalt as the nitrate, 1 pound mole.

lProceed as in Example 5, steps 2 through 11. Similar results areobtained.

In Step 1 of the procedure, the cobalt nitrate canbe replaced by anequimolar amount of copper, nickel, iron, zinc, cadmium, tin, or bismuthsulfate, nitrate, chloride, or acetate with comparable results.

EXAMPLE 18 (1) Dissolves 110 pounds of metallic manganese as the nitratein 750 gallons of water. Dissolve also in this same solution 60 poundsof nickel as the nitrate.

(2) Slurry also in this solution 200 pounds of chromium hydroxide,Guignets green.

(3) Add Water to bring the volume to 800 gallons and heat to raise thetemperature to 35 C.

(4) Agitate vigorously while adding vaporized anhydrous ammonia untilprecipitation is complete. Stir the slurry for one hour and filter. Washthe filter cake with water.

(5) Apply filter cake to a refractory support, activated alumina in theform of three to six mesh granules.

(6) Heat in air at 400 C. for two hours. The catalyst as thus preparedcan be used for the treatment of combustion gases from hydrocarbonfuels, particularly such as those in diesel installations and powerplants.

In the foregoing example, similar catalysts are prepared by usingditferent supports instead of the activated alumina. Thus the procedureas described is followed but the coating is applied to:

17 (1) Porous ceramic spheres, tablets, or rings of porous ceramic, (2)Etched nickel, Nichrome, and Inconel wire, (3) Silica gel, (4)Silica-alumina, (5 Alundum, (6) Pumice, (7) Diaspore, (8) Bauxite, (9)Periclase, (10) Zirconia, (11) Titania, (12) Diatomaceous earth, (13)Calcium sulfate, (14) Barium oxide, and (15) Calcium oxide.

EXAMPLE 19 (1) Dissolve 110 pounds of metallic manganese as the nitratein 750 gallons of water. Dissolve also in this same solution 32 poundsof copper as the nitrate and 30 pounds of nickel as the nitrate.

(2) Slurry in this solution 200 pounds of alumina hydrate, 0.5 micronparticle size.

(3) Dissolve also in the solution 300 pounds of chromic acid anhydride.Add Water to bring the volume to 800 gallons and adjust the temperatureto 35 C.

(4) Stir vigorously while adding vaporized anhydrous ammonia untilprecipitation is complete. Continue to stir the slurry for one hour andthen filter. Wash the filter cake with water and dry.

(5) Calcine the dried product at 400 C. for one hour.

(6) Into a sigma-arm mixer charge 100 pounds of the product producedabove together with 65 pounds of water in which is dissolved 13 poundsof aluminum oxide as the nitrate. Knead until the mass is homogeneous.

(7 Dry and pulverize the product and pellet it.

(8) Heat the pellets in air at 400 C. for three hours. The heatingconverts the aluminum nitrate to the oxide. Under the conditionsdescribed the crystallite size of the manganite, the chromite, and thealumina is of the order of 50 Angstroms. If the catalyst is heated foran extended time at temperatures around 750 C. or above, there is agrowth of particle 'size up to several hundred Angstroms. In thepresence of significant quantities of silica the crystallite size willgo as high as 400 Angstroms or even higher. If the crystallite size ismarkedly above 400 Angstroms, the products produced by such an exampleare not to be preferred.

Further products of the invention can be made by replacing the aluminumnitrate in Step 6 with a molecularly equivalent weight of hydroustitania gel, thorium nitrate, cerium nitrate, calcium hydroxide, calciumnitrate, calcium acetate, magnesium hydroxide, barium hydroxide, bariumnitrate, and aluminum nitrate. :Molecularly equivalent weights of thefollowing can similarly be used: aluminum alcoholates like the ethylate,butylate, and propylate, zircon powder, aluminum hydroxide gel,zirconi-a gel, and cerium oxide.

EXAMPLE 20 (1) Dissolve 165 pounds, 3 moles, of metallic manganese asthe nitrate in 750 gallons of water.

(2) Dissolve also in the same solution containing the manganese, 100pounds, 1 mole, of chromic acid anhydride.

(3) Slurry in this solution 200 pounds of alumina hydrate, 0.5 micronsize, low sod-a content.

(4) Add water to bring the volume to 800 gallons and heat to raise thetemperature to 35 C.

(5) Agitate vigorously while adding vaporized anhydrous ammonia througha diifusion sparger at two pounds per minute until precipitation iscomplete as evidenced 18" by no further addition of ammonia producing nofurther" precipitate. v

6) Stir the slurry for one hour and then filter. Wash the filter cake,in situ, with water.

( 7) Dry the filter cake at 135 C. for one hour.

(8) Raise the temperature to 400 C. and calcine at that temperature forone hour to convert the manganate salts to mangano-chromic manganitesand the alumina hydrate to alumina, each having crystallite sizes ofabout 50 Angstroms.

(9) Charge a pound lot produced as above, together with 65 pounds ofwater in which is dissolved 13 pounds of ammonium chromate into asigma-arm mixer and knead until the mass is homogeneous and clay-like.Alternatively a similar product can be made using 33 pounds of ammoniumchromate in this step.

(10) Dry and pulverize the product and mix with 1% of finely dividedgraphite. Pellet to form by inch cylindrical tablets.

(11) Heat the pellets in air at 400 C. for three hours to effectstructural orientation without significantly increasing the crystallitesize of the mangano-chromia manganite, the alumina, or the other crystalspecies contained. The catalyst can be used for fume abatement.

EXAMPLE 21 Prepare a catalyst as in Example 20 through Step 8 thenproceed according to the following procedure.

(9) Charge an 80 pound lot produced as above together with 20 pounds ofa separately prepared coppernickel chromite (CuO-CuCr O NiO-NiCr O and65 pounds of water in which is dissolved 33 pounds of ammonium chromateinto a sigma-arm mixer and knead until the mass is homogeneous andclay-like.

The nickel and copper chromite were prepared as follows:

as evidenced by further addition of ammonia produc ing no furtherprecipitation.

(e) Agitate the slurry for one hour and then filter; Wash the filtercake with water. I

(f) Dry the filter cake at 150 C. for 8 hours.

(g) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the basic chromate salts tochromites having a crystal lite size of about 50 Angstroms.

(10) Dry for 16 hours at 250 C. then pulverize the product and mix with1% of finely divided graphite. Pellet to form by inch cylindricaltablets.

The catalyst as thus prepared can be used directly as in acatalyticmufiier for an internal combustion engine. The heat of thegases will eflFect the desired heat treatment but this is not preferredbecause the catalyst may incidentally be subjected to liquid water withsome damage. It is better before use to heat the catalyst 250 or 300 Cfor three hours.

EXAMPLE 22 1) Dissolve pounds, 2 pound moles, of metallic manganese asthe nitrate in 750 gallons of Water. Dissolve also in this same solution32 pounds, 0.5 pound mole, of copper as the nitrate and 30 pounds, 0.5pound mole, of nickel as the nitrate.

(2) Slurry in this solution 200 pounds of alumina hydrate, 0.5 micronsize, low soda content.

(3) Dissolve also, in the same solution containing the manganese andcopper nitrates and alumina hydrate, 300 pounds, 3 pound moles, ofchromic acid anhydride (CrO (4) Add water to bring the volume to 800gallons and heat to raise the temperature to 35 C.

(5) Agitate vigorously while adding vaporized anhydrous ammonia througha distributor at two pounds per minute until precipitation is completeas evidenced by further addition of ammonia producing no furtherprecipitation.

. (6) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(7) Dry the filter cake at 135 C. for one hour.

(8) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the manganate salts tomangano-chromia-manganite having a crystallite size of about 50Angstroms. The alumina and copper chromite formed are of similar size.

(9) Charge a 100 pound lot produced as above, together with 65 pounds ofwater in which is dissolved 33 pounds of ammonium chromate into asigma-arm mixer and knead until the mass is homogeneous and clay-like.

(10) Dry and then calcine at 300 C. and then pulverize the products andmix with 1% by weight of finely divided graphite. Pellet to form by inchcylindrical table-ts.

(11) Heat the pellets in air at 400 C. for three hours to effectstructural orientation without significantly increasing the crystallitesize of the mangano-chromiamanganite, the alumina, the copper chromiteor the chromic oxide contained.

Thirty-three pounds of a product prepared as above is placed in amuffler designed for catalytic conversion of exhaust gases of anautomobile. The mufi'ler is similar to a conventional auto muffler withexhaust intake and outlet and provided with dividing vertical baffieswhich form transverse chambers into which the catalyst is placed.Cooling tubes carrying ambient air runs through the length of themufller and keep the temperature from becoming excessive. An aircompressor driven by the car motor supplies about 30% excess, or more,over that stoichiometrically required for the oxidation of the exhaustgases.

The muffier as described was installed on a 1958 Oldsmobile having a V-8cylinder engine. This was operated for 15,814 miles over typical terrainencountered in the eastern part of the United States. The light-offtemperature of the catalyst as it was applied to the car was about 150C. Under idling conditions of the motor the CO clean-up was in excess of90%. Clean-up of olefinic and paraflinic hydrocarbons in the automobileexhaust under idling conditions was also in excess of 90%. The enginewas operated at various speeds up to and in excess of 50 miles per hourbut at 50 miles per hour a test of the completeness of clean-up of thecarbon monoxide olefinic and parafiinic carbons was examined. Underthese conditions C-O removal was in excess of 95% and a high degree ofclean-up was obtained for the hydrocarbons.

The automobile was periodically examined for performance of the catalystafter every thousand miles. At the end of 15,814 miles the light-offtemperature was about 250 C. Under idling conditions the carbon monoxideclean-up was in excess of 90% and the hydrocarbon clean-up was in excessof 60%. Also, after this same period of usage the automobile wasexamined at 50 miles per hour and carbon monoxide clean-up was in excessof 80% and hydrocarbon clean-up was in excess of 80%.

EXAMPLE 23 (1) Dissolve 110 pounds, 2 pound moles, of metallic manganeseas the nitrate in 750 gallons of water. Dissolve also in this samesolution 32 pounds, 0.5 pound mole, of copper as the nitrate and 30pounds, 0.5 pound mole, of nickel as the nitrate.

(2) Slurry 300 pounds of alumina hydrate 0.5 micron size low sodacontent in 200 gallons of water in which is dissolved 150 pounds ofnitric acid, HNO This nitric acid solution with an alumina hydratesuspension is heated to the boiling point and maintained at thistemperature for 3 hours. It is then cooled to 50 C. and added to thenitrate solution described in item 1. The heat treatment converts atleast a portion of the alumina to the boehmite crystal form and in theform of small colloidal platelets.

(3) Dissolve also, in the same solution containing the manganese andcopper nitrates and alumina hydrate, 300 pounds, 3 pound moles, ofchromic acid anyhydride (CrO' (4) Add water to bring the volume to 800gallons and heat to raise the temperature to 35 C.

(5 Agitate vigorously while adding vaporized anhydrous ammonia through adistributor at two pounds per minute until precipitation is complete asevidenced by further addition of ammonia producing no furtherprecipitation.

(6) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(7) Dry the filter cake at C. for one hour.

(8) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the manganate salts tomangano-chromia manganite having a crystallite size of about 50Angstroms. The crystallites of the alumina, and of the copper and nickelchromites formed, are of similar size.

(9) Charge a 100 pound lot produced as above, together with 65 pounds ofwater in which is dissolved 10 pounds of magnesium acetate into asigma-arm mixer and knead until the mass is homogeneous and clay-like.

(10) Dry and pulverize the product and mix with 1% of finely dividedgraphite. Pellet to form by 7 inch cylindrical tablets.

(11) Heat the pellets in air at 400 C. for three hours to effectstructural orientation without significantly increasing the crystallitesize of the mangano-chromia-manganite, the alumina, the copper chromiteor the chromic oxide contained.

The crystallite size of crystallites in the product was less than 50-60Angstroms and this product had a small crystallite size even afterextended heating at 800 C. This is shown by X-ray examination whichshows the crystallite size after three hours at 800 C. to be under 500Angstroms. This catalyst has very high activity even after extendedheating.

EXAMPLE 24 The series of steps described above in Example 22 werefollowed exactly except that Step 2 was as follows:

(2) Slurry in the above solution 200 pounds of a silica aerogel having aparticle size below one-half micron. There can be used instead an equalweight of aerogel of the Kistler Patent 2,093,454 or of a fumed productmade by volatilizing silicon chloride and hydrolyzing. Alternativelysilica sols can be used to introduce an equivalent weight of silica ofcolloidal size such as those sols shown in Bechtold and Snyder2,574,902, Rule 2,577,484, Davisons Legal Patent 2,724,701, andMonsantos White Patent 2,375,738.

The catalyst produced according to this example can be used as are theothers of the invention but it finds its principal utility when used attemperatures no higher than about 700 C.

EXAMPLE 25 (1) Charge 500 pounds of 4 to 8 mesh activated alumina to acylindrical vessel which is completely closed except for valved openingsat the bottom and top of the vessel.

(2) Force superheated steam at to 250 C. through r 21 the bed ofactivated alumina until the entire bed of activated alumina is above 125C.

(3) In a separate vessel prepare, and adjust to 30 C., 1000 gallons(sufiicient to completely fill the vessel of Item 1 and allinterconnecting piping) of an aqueous solution composed of 3000 partswater, 110 parts manganese as the nitrate, 33 parts copper as thenitrate, 30 parts of nickel as nitrate, and 300 parts chromic acidanhydride, CrO

(4 After the activated alumina has been uniformly heated to above 125 C.close the exit port of the vessel containing the alumina and thensimultaneously close the inlet steam valve and open the valve admittingthe solution prepared in Item 3 above.

(5) As the temperature in the vessel drops below the point at whichcondensation of the steam atmosphere takes place, the solution will bedrawn into the vessel and into the interstices and pores of theactivated alumina.

(6) After the solution has remained on the granules for minutes, openthe top port and drain the excess solution from the granules.

(7) Feed into the granules a gaseous mixture composed of 3% anhydrousammonia in nitrogen until there is no further reaction of ammonia withthe granules and with the adsorbates on the granules. This point can bedetermined both by lack of temperature rise as the gases pass throughthe granules and by the breakthrough of ammonia in the exit gas. Thetemperature of the incoming gas mixture and the percentage of ammonia inthe gas can be varied to control the temperature of the granules withinthe range of 4070 C.

(8) Stop the flow of ammonia-nitrogen mixed gas and feed heated air tothe vessel. Raise the temperature of the granules to 300 to 400 C. andmaintain this range for one hour. The off-gas from the vessel can beprocessed for the recovery of valuable salts and dust evolved from thegranules during this calcination.

(9) Discharge the impregnated and calcined granules. Catalyst preparedaccording tothis example is useful for fume abatement.

A similar catalyst can be made in which the activated alumina is firsttreated with an aqueous solution of potassium carbonate containing 2grams of potassium carbonate per liter. Thereafter the excess potassiumcarbonate solution is drained off and the granules are dried to leavethe potassium carbonate on the surface. The remainder of the process ofthe above example can be followed just as shown.

Instead of using the indicated amount of potassium carbonate similarresults can be obtained using sodium carbonate, lithium carbonate,calcium hydroxide, barium hydroxide, and other alkalis shown above, theamounts in each instance being those just indicated.

EXAMPLE 26 (1) Dissolve 275 pounds, 5 pound moles, of metallic manganeseas the nitrate in 750 gallons of water. Dissolve also in this samesolution 32 pounds, 0.5 pound mole, of copper as the nitrate and 30pounds, 0.5 pound mole, of nickel as the nitrate.

(2) Dissolve also in the same solution 200 pounds, 2 pound moles, ofchromic acid anhydride (CrO (3) Add water to bring the volume to 800gallons and heat to raise the temperature to 35 C.

(4) Agitate vigorously while adding vaporized anhydrous ammonia througha distributor at two pounds per minute until precipitation is completeas evidenced by further addition of ammonia producing no furtherprecipitation.

(5) Stir the slurry for one hour and then filter. Wash the filter cakewith water.

(6) Dry the filter cake at 135 C. for hour.

(7) Raise the temperature of the dried product to 400 C. and calcine atthat temperature for one hour to convert the manganese salts tomahgano-chromia-manganites having a crystallite size of about 50Angstroms. At the same time the calcination converts manganese hydroxideto manganese oxides which serve as potential components of the ioniccrystals and lend desired properties. These are present because anexcess of manganese is used in Step 1 over that required to formmanganese chromite of MnzCr ratio of 3:2. The calcination also convertsthe basic nickel and copper chromates to chromites.

(8) Charge a pound lot produced as above, together with 65 pounds ofwater in which is dissolved 40 pounds of anhydrous aluminum nitrate intoa sigma-arm mixer and knead until the mass is homogeneous and claylike.

(9) Dry the product and calcine at 400 C. for 2 hours to decompose thenitrate and form aluminum oxide, pulverize and mix with 1% of finelydivided graphite. Pellet to form /8 by A; inch cylindrical tablets.

(10) Heat the pellets in air at 400 C. for 3 hours to effect structuralorientation.

The product prepared as above can be used effectively for the catalyticconversion of exhaust gases of an automobile. Like many other of theexample catalysts, this is particularly good for use at high temperatureand has a very low light-off temperature. It can accordingly be used toraise the temperature of exhaust gases of an automobile to make themmore suitable for conversion in a conventional catalytic rnufiler orother device.

Catalysts of similar utility and character can also be made replacing inStep 8 the aluminum nitrate there used with the same weight of thoriumnitrate, cerium nitrate, magnesium nitrate, lanthanum nitrate, and anyother of the interspersants above described.

EXAMPLE 27 (l) 250 parts by weight of chromic acid anhydride and partsby weight of NH are dissolved in 610 parts by weight of water.

(2) A second solution is made containing 77 parts by weight of manganeseas manganese nitrate and 923 parts by weight of water.

(3) 300 parts by weight of activated bauxite of 4 to 8 mesh granules isplaced in a perforated basket and dipped into the solution prepared inItem 1 above. It is then removed, drained for three minutes and thendipped into the solution described in Item 2 above. After remaining inthe solution for about 1 minute the basket is removed and the bauxite isdrained and dried. It is noted that the activated bauxite is an articleof commerce which is prepared by heating bauxite ore under oxidizingconditions.

(4) The dried granules are then heated to 250 C. for 30 minutes. Theyarethen cooled. The catalyst thus prepared has a ratio MnzCr of 3:52. It isto be noted that the MnzCr ratio is that of the reactants used becauseunlike aqueous precipitations there is no loss of chromium during theprocessing. The catalyst is useful for oxidation and reduction reactionsat elevated temperatures and is particularly useful for the treatment ofautomobile exhaust gases.

EXAMPLE 28 A procedure was followed as in Example 27 except for thefollowing differences:

(1) The first solutionl00 parts of chromic acid anhydride, and 28 partsof NH are dissolved in 886 parts of water.

(2) 220 parts of manganese as manganese nitrate are dissolved in 780parts by weight of water.

(4) The catalyst produced carries a mangano-chromiamanganite having anMnzCr ratio of 3:0 .75.

EXAMPLE 29 Catalysts are prepared as in Examples 27 and 28 above butmaking the following changes in the numbered items: (1) In the firstsolution in each of Examples 27 and 28 23 there is included anadditional 100 parts by weight of chromic acid to supply the chromiumrequired for the copper and nickel chromites to be formed.

(2) To the second solution there is added 25 parts by weight of copperas copper nitrate and 20 parts by weight of nickel as nickel nitrate.

Other co-catalysts as described above can similarly be used in thesecond solution.

(3b) The dried catalyst is then calcined at 250 C. for 30 minutes. Theresulting catalysts are suitable for use in oxidation and reductionreactions and especially for treating automobile exhaust gases. Insteadof the final calcination one can instead rely upon the heat present inthe catalytic reactor as is, of course, true in the numerous examplesabove, but it is ordinarily preferred to effect the calcination as heredescribed.

If the product is to be used in an automobile exhaust mufiler withoutprior calcination, it would be preferred to use the acetate of theinterspersant rather than the nitrate and, of course, other salts whichwould give unobjectiona'ble products of combustion can "be used as cancolloids which do not need to decompose further such as alumina sols.

Any of the interspersants above described can, of course, be used inthis last step in amounts as already taught above.

It will aslo be understood that in following the procedure in thepresent example, the first interspersant as described in Example 30 canbe omitted so that only the interspersant of Step 3a is used.

It is further to be understood that in any of Examples 27 through 31 onecan use the same weight of any of the other supports previouslydescribed. Thus the procedure as shown in the examples can be carriedout using the indicated weight of alundum as granules, activated aluminaas granules, and titania granules.

EXAMPLE 30 Catalysts are prepared as in Examples 27, 28, and 2.9 abovebut inserting the following steps after Item 3:

(3a) A third solution is prepared using 54 parts by weight of aluminumas aluminum nitrate dissolved in 946 parts by weight of water. Thedrained catalyst from Item 3 is placed in this third solution for 1minute, removed, and drained before the drying step described above.

It will be understood that instead of using aluminum nitratewhichresults in aluminum oxide as an interspersantthere can instead be usedany of the other interspersants described above. These can of course beadded as colloids or as heat decomposable salts.

EXAMPLE 31 The processes of each of Examples 27, 28, 29, and 30 can bemodified by the addition of an interspersant after calcination. This canbe done by inserting in the sequence of items given in each of theforegoing examples the following:

(4a) A solution is prepared by dissolving 69 parts by weight of bariumas barium nitrate in 931 parts by weight of water. The calcined catalystfrom the preceding step is dipped into this solution, allowed to remainfor 1 minute, removed, drained and dried.

EXAMPLE 3 2 (1) 165 parts by weight of manganese as the nitrate, 600parts by weight of chromic acid anhydride, 500 parts by weight ofaluminum hydrate as finely divided powder, 28 parts by weight of nickelas the nitrate, and 31 parts by weight of copper as the nitrate, are alldry-mixed togeth'er.

(2) The mixture is agitated and simultaneously heated and a reducing gascomposed of hydrogen and CO diluted with nitrogen is fed to the mixingarea and the fusion is continued until the mass has finished reactingand has solidified.

2 1 (3) The solidified product is cooled, crushed, and screened toproduce a catalyst particularly useful for treatment of automobileexhaust gases.

EXAMPLE 3 3 A catalyst was prepared as in Example 32 with the exceptionthat prior to the heating of Step 2, 7000 parts by weight of alumina as4 to 8 mesh activated granules is also incorporated into the mixture toact as a support material.

The invention claimed is:

1. A process for treatment of automobile exhaust gases comprisingpassing said gases over a catalyst which is mangano-chromia-manganite,the .crystallites of which are kept apart by crystallites of arefractory which melts above 1000 C., said mangano-chromia-manganitebeing a complex product of the character described having the empiricalformula:

XCr O 2YMnO where the ratio of Y:X=3:0.5 to 3:30 11:2, 3, and 6, andm=1, 1.33, 1.5, 2, and 2.5,

the formula being a summation of the proportion of its content of MnO,MnO Mn O Mn O M11 0 Cr O CI203'MI102, CI'O'MI1203, CYO3MHO, C'I203M1'10.

2. A process as defined in claim 1 wherein the exhaust gases are firstmixed with air and then passed over the mangano-chromia-manganitecatalyst to oxidize carbon monoxide and hydrocarbons.

3. A process as defined in claim 1 wherein the exhaust gases are firstpassed over a portion of the manganochromia-nianganite catalyst toreduce nitrogen oxides, then air is added to the treated gas stream andthe mixture is passed over a second portion of themanganochromia-manganite catalyst to oxidize carbon monoxide andhydrocarbons.

4. A process as defined in claim 1 wherein the mangano-chromia-manganite is composed of aggregates of crystallites no larger than1000 Angstroms.

5. A process for treatment of automobile exhaust gases comprisingpassing said gases over a mangano-chromiamanganite catalyst of thecharacter described having the empirical formula:

XCr O 2YMnO where the ratio of Y:X:3:0.5 to 321.5 and 3:3.5 to 3:30,11:2, 3, and 6, 171 1, 1.33, 1.5, 2, and 2.5,

the formula being a summation of the proportion of its content of MnO,MnO Mn O Mn O Mn O Cr O Cr O -MnO CI'OMIIzOg, CIO3'MI10, Cl'203MI10.

6. A process as defined in claim 5 wherein the mangano-chromia-manganiteis composed of aggregates of crystallitcs no larger than 1000 Angstroms.

References Cited by the Examiner UNITED STATES PATENTS 2,025,140 12/1935Wenzel 23-2 OTHER REFERENCES Mellor, A Comprehensive Treatise onInorganic and Theoretical Chemistry, Longmans, Green & Co., New York,N.Y., volume 12, 1932, pages 274 and 280.

Sidgwick, The Chemical Elements and Their Compounds, Oxford UniversityPress, London, volume 2, 1950, page 1273.

OSCAR R. VERTI Z, Primary Examiner.

EARL C. THOMAS, Examiner.

1. A PROCESS FOR TREATMENT OF AUTOMOBILE EXHAUST GASES COMPRISINGPASSING SAID GASES OVER A CATALYST WHICH IS MANGANO-CHROMIA-MANGANITE,THE CRYSTALLITESS OF WHICH ARE KEPT APART BY CRYSTALLITES OF AREFRACTORY WHICH MELTS ABOVE 1000*C., SAID MANGANO-CHROMIA-MANGANITEBEING A COMPLEX PRODUCT OF THE CHARACTER DESCRIBED HAVING THE EMPIRICALFORMULA: